This invention is generally directed to systems which correct the phase and amplitude of the color components of television signals. It is particularly directed to systems such as television receivers which employ a VIR (Vertical Interval Reference) signal to effect such correction.
Many television stations broadcast a VIR signal on the nineteenth line of each television field. That signal is processed in some television receivers for use in correcting the phase of the color bursts and the amplitude of the chrominance which are transmitted during the receiver's scan time.
An important aspect of such correction systems is that they apply phase or amplitude adjustment only when needed. That is, color signals which do not require adjustment should be unmodified by the correction system so that the reproduced television image has correct saturation and hue.
The design criteria set forth above may be particularly difficult to achieve in a type of correction system referred to herein as a "feed through" system. In this type of system, the color signal is applied to a phase and amplitude correction network which is instructed either to feed the color signal directly through to further color processing circuitry without modification, or to modify the color signal when other circuitry senses the presence of phase or amplitude errors. Because the phase and amplitude correction network always handles the color signal, even when correction is not required, it is difficult to avoid introducing unwanted phase, amplitude and/or bandwidth distortions. The present invention provides a phase and amplitude correction network which avoids this problem and makes VIR correction a feature which is more easily incorporated in a television system.